I had a Plex server setup that could do that. It was an old spare computer. iTunes can (could?) do that over a lan. That’s how the very first hard drive AppleTV worked.

It was a pain to maintain and had symmetrical gigabit internet. Most people have cable internet with very low upstream bandwidth.

But now you’re asking them to buy another device and what’s the benefit for them?

In today’s world, I would buy an Nvidia Shield that can do hardware transcoding.

But you can already download video to mobile devices ahead of time.